Computer for estimated time of arrival



July 28, 1953 o. H. scHucK COMPUTER FOR ESTIMATED TIME OF ARRIVAL 2 Sheets-Sheet 1 Filed Nov. 29. 1948 [IT VVENTOR OSCAR H- $CHUCK BY M wozommwm .pzuzm au 02.55/52 M02455 July 28 195 3 0. H. scHucK COMPUTER FOR ESTIMATED TIME OF ARRIVAL 2 Sheets-Sheet 2 Filed NOV. 29, 1948 INVENTOR. OSCAR u. SCHUtK HTTORNE'Y Patented July 28 1953:

COMPUTER FOR ESTIMATED TIlWE OF ARRIVAL Application November 29, 1948, Serial No. 62,482

11 Claims.

This invention relates to the field of air navigation, and more particularly to means giving the pilot of a craft a continuous indication of the time at which he can expect to reach a desired detination, if he continues to approach it at his existing rate. This time is referred to herein as estimated time of arrival, and if the estimated time of arrival of every craft approaching a given airport is known at the control tower while the craft are still some distance away, minor adjust- .ments can be directed to cause the craft to reach the airport in an orderly succession at such intervals as obviate the need for stacking.

It is an object of the present invention to provide means for obviating stacking of craft at an airport by giving continuous information as to the estimated time of arriva1 of craft approaching the airport, for radio transmission to the control tower.

It is an object of the invention to provide an improved navigational instrument for computing the estimated time of arrival of a craft when its ground speed and distance to destination are known.

It is another object of the invention to provide radio means for giving outputs in accordance with the ground speed and distance to destination of a craft approaching the radio ground station as a destination, and means for continuously computing the estimated time of arrival of the craft from these outputs and a further output varying with present time, as well as for displaying the estimated time of arrival so computed.

It may happen that several craft are approaching an airport at such distances and rates that their estimated time of arrivals are the same. In such a case, when the reports are received at the control tower, instructions must be given to all but one of these craft to change their approaches so that the proper interval may intervene between their arrival times. The change may be only a moment or two, if the airport is not busy, but it may be that a considerable change may have to be made in the estimated time of arrival of a craft to bring it to the airport at a time when the landing facilities will be free for use.

When a new estimated time of arrival is assigned to the craft, the question arises as to whether it can be flown to make good the new time. Every craft has maximum and minimum safe limits on its air speed, and for any given distance between the craft and the airport these limits determine the earliest and latest times at which a craft in direct flight can reach the airport. For example, a craft having a normal cruising speed of 200 miles per hour can be flown over reasonable periods as fast as 240 miles per hour, or as slow as miles per hour. Higher speeds are dangerous to the engines; lower speeds approach stalling conditions too closely for safety. If a new estimated time of arrival would require an air speed outside these limits, it cannot be accomplished, and a substitute assignment must be requested.

It is a further object of the invention to embody in a device such as previously described, means whereby the displayed estimated time of arrival can be temporarily set to any assigned value, the new ground speed and air speed required to make good the new estimated time of arrival being automatically displayed at the same time.

A further object of the invention is to provide an estimated time of arrival computer in part energized continuously according to the crafts distance to destination, and in part energized alternatively either from an output varying with ground speed, or from a manually adjustable control knob which substitutes an arbitrary variable for the responsive variation in ground speed, and which is also effective when operated to in terrupt the normal operation of an airspeed indicator and change its indication by the amount of the arbitrary variation.

Yet another object of the invention is to provide a number of telemetric systems together with switching means for interrelating them in either of two fashions, a first in which a first transmitter drives a first receiver and a second transmitter drives second and third receivers and also drives a third unit as a receiver, and a second in which the first and second transmitters are deenergized, and all receivers are driven by the third unit acting as a transmitter.

Various other objects, advantages, and features of novelty which characterize my invention are pointed out with particularity in the claims and executed to and forming a part hereof. However, for a better understanding of the invention, its advantages, and objects attained by its use, reference should be had to the subjoined drawing, which forms a further part hereof, and to the accompanying descriptive matter, in which I have illustrated and described a preferred embodiment of my invention.

In the drawing:

Figure l is a diagrammatic showing of the components making up a system according to. the invention; and

Figure 2 is a fragmentary showing of components making up a portion of the structure of Figure 1.

In the foregoing discussion, and in that which follows, the word arrival is applied, not in the sense of an airplane coming to rest on the ground at 2. terminus, but in the sense of an aircraft reaching a particular point in the air from which the final let-down may take place. Let it be assumed that an aircraft is at a distance 11. from its destination or point of arrival, and that its component of movement toward the destination If the present time T then the estimated time or arrival at the destination if present conditions m flight are maintained, :is given by the expression yr E.T..A.=T. 2

{It thus apparent that in order to compute the estimated time of arrival of acraft, it isnecessar-y to know as variables its distance from the destination in question, its ground speed with respect to that distance, and th present time,

A system for use in practicing the invention is shown in Figure -1. The computer proper is shown to comprise a balancea-ble network it, a balancing motor -I l, a ground speed motor 52, and a panel board i3 including counter type indicators 14, I5, 56 and I1, which give indication of present time, estimated time of arrival, ground speed, and airspeed, respectively- :Distance to destination and ground speed information are provided to th computer from a Distance Measuring Equipment installation, which is shown to comprise an interrogator l9 and a converter 23 carried in the craft, and a responder 2| located at a fixed position on the ground. Thedistance to destination output from converter-Ell appears as mechanical rotation of a shaft and the ground speed output appears as a voltage between a pair-or" conductors 23 and 25. Converter -26 is energized by connection at 2-5 to suitabl supply of alternating voltage, controlled =byra master switch -26. Connection .255 will hereafter be referred to as a source of alternating voltage. Other portions of the system are energized from the same source through conductors 2'! and til. The nature of members 2i and 22 will be recited in more detail in connection with Figure 2.

Rotation of shaft 22 moves the slider 31 of a voltage divider 32 with respect to its winding 33. Winding 33 is connected to the seoondary'winding 36 ofa transformer 35 whose primary winding 36 is energized from source through conductors 2-? and 3,9. The voltage between slider and a conductor 3 connected to one terminal of winding- 33 therefore depends upon the position of slider 31 along the winding.

Voltage divider 32 comprises a portion of balanceable network 1 0, which also includes further potential dividers 40 and 41 having windings l2 and 43 and sliders 44 and 45 all respectively. Winding is connected to the secondary winding d5 of a transformer 4'! whose primary winding 5* is energized from source 25 through conductors El and 3d. Conductor 31 is connected to one terminal of winding 42, and also to one terminal of winding. 43, the other terminal of which is connected to slider 44 of voltage divider 40. Slider d5 of voltage divider 4| is thus at a potential, with respect to conductor 31, which depends on the positions of sliders M and 15 along their respective windings.

Sliders 3i and 45 are connected to the input conductors 5i and 52 of a motor control amplifier t3, supplied with power from source 25 through conductors 27 and 30. The output of amplifier 53 energizes motor H through a suitable cable '54, :and motor H moves slider 55 with respect to winding '43 through a suitable mechanical connection- B-Ea.

Slider d4 of voltage divider so is actuated by ground speed motor 12 through a suitable mechanical connection 56. Operation of motor (2 is controlled through a complex telemetric system alternatively the y voltage appearing between conductors 23 and a l, 01' by manual operation of alknob 251, the interconnection being controlled by 'a pair of relays and 6 1. These relays, together with 221, further relay 2 and an electromagnetic clutch indicated at in control the interrelation of a number of self-synchronous 'dynamoelectric machines which act as tramsmitters "and receiversein the complex telemetric system. These machines are indicated "at 1, 5, '66, El, 70 and '74. Each machine includes :a single-phase winding and a three-phase winding. As shown in connection with machine 64, the single-phase winding is indicated by the reference numeral 64a and the three-phase windingby the reference numeral Mb: the singleand threephase windings of the other units are indicated by the :same :suifix letter system.

Single-phase windings G la, 55a, a, and We are energized from source 25 through conductors 2i and 30,, to provide input energy for the telemetric system. Outputs from the system are obtained fromsingleephase windings iil'a and Ma.

Three-phase winding B ll) is rotated by :a mechanical connection 38 to an air speed sensing :unit 12, connected .to the usual Pitot-static tube 13. Winding 6% is connected with winding 54?? through relay 62 which functions :as a triplepol'e single-throw normally closed switch. llhe voltages at the terminals of winding 64b are determined in amplitude by the rotated position of that winding with respect to winding (Sea, and hence by the air speed sensed by member d2. When relay 62 is in its :deenergized or normal condition, as shown in Figure 1, these voltages are conducted to the terminals of winding 66?); winding 661i is continuously energized, so w inding 65b is driven to a rotated position which :is determined by the voltages on the terminals of the windings. At the same time the setting of air speed indicator H is also changed, by amechanical connection it, and if a given relationship is once established between the positions of windings 64b and 'Bdb, with respect "to windings 64a and 66a, and the reading of indicator ii, the reading is thereafter correct for all changes in air speed as sensed by member I2.

Mechanical connection "i4 also extends to one side oi a. normally deenergized electromagnetic clutch 15, which is :of the type transmitting mechanical energy only when suitably energized. The clutch is deenergized and energized simultaneously with relay 2, so that when electrical control of winding 6512 is interrupted by :rel'ay t2,

mechanical control of the winding may be brought about through clutch I5.

Ground speed motor I2 is controlled through an intricate circuit including the ground-speed output voltage appearing at conductors 23 and 24 as previously indicated. This voltage is supplied to an amplifier I6, energized from source 25 through conductors 21 and 30, in series with the output from a velocity generator 11 and that from a voltage divider 86. Velocity generator TI is energized from source 25 through conductors 21 and 36, and is driven by a motor 8| connected to amplifier I6 by a suitable control cable 82. Voltage divider 86 is shown to comprise a slider 83 movable with respect to winding 84 by mechanical connection to motor 8|. Winding 84 is energized from the secondary winding 85 of a transformer 86 whose primary winding 81 is energized from source 25 through conductors '21 and 30. Members I6 to 81 inclusive comprise a smoother identified by the general reference numeral 96, and functioning to position the shaft of motor 8| in accordance with the general value of ground speed represented by the voltage appearing between conductors 23 and 24, while preventing the motor from following transient er-' ratio changes in that voltage, such as are frequently found to occur in the output from unit 26.

Motor 6| is arranged to drive winding 10b through a suitable mechanical connection 9|. The voltages at the terminals of winding 101) are determined by the rotated position of the shaft of motor 8|, that is, by the magnitude of the groundspeed signal appearing at conductors 23 and 24.

Relay 60 functions as a triple-pole singlethrow switch. In its normal or deenergized condition it completes the circuit from winding 'IIlb to winding 60b, and the position of winding 65b is thus determined by the position of winding 161). In the energized position of relay 60, this connection is interrupted.

Relay 6| functions as a triple-pole doublethrow switch. In the normal or deenergized condition of relay 6|, winding IIJb is connected to windings 671) and III) so that the positions of these windings are determined by the positionof winding 16?), that is by the ground speed signal appearing between conductors 23 and 24. In the energized condition of relay 6|, the connection of windings 61b and III: to winding 161) is interrupted, and windings 61b and Nb are instead connected to winding 65b: the positions of windings 61b and III; are now determined by the pe sition of winding 65b. The latter is rotatable by a manual knob 51: relays 60 and 6| are energized at the same time, so that when windings 61b and I It are connected for control in accordance with the position of winding 65b, the latter is disconnected from its normal control by winding 16b.

Winding IIa is not energized from source 25, but instead is connected to the input of an amplifier 92 energized from source 25 through conductors 21 and 36. Unit II thus acts not a a generator, such'as unit 64, or as a motor, such as unit 66, but as a transformer, the voltage supplied to amplifier 92 being determined bythe rotated position of winding 'IIb with despect t winding Ila, and the voltages supplied to winding IIb. Amplifier 92 is connected through a suitable cable 93 to control the operation of ground speed motor I2 which acts through mechanical connection 56, not'only to move slider 44 along winding 42, but also to'readjust the'p0-' motor I I'.

sition of winding 'IIb until the voltage induced in winding 'I la becomes zero, when operation of the motor stops. The motor is also connected by a suitable mechanical means 94 to drive groundspeed indicator I6 on panel I3.

Unit 67 also functions as a transformer rather than as a rotating machine, so that the voltage impressed on the input terminals of an amplifier 95 is determined by the rotated position of winding 61?) with respect to winding 61a, and the voltages supplied to winding 61b. Amplifier 95 is energized from source through conductors 2'! and and controls a motor 96 through a suitable cable 91. Motor 96 acts through a mechanical connection I06 to adjust the rotated position of winding 61b so that no voltage appears in winding 61a. When this condition is reached operation of motor 96 stops. Mechanical connection I06 is also extended to clutch I5. As previously pointed out, this clutch is normally disengaged, so that there is no connection between shafts I4 and I00. Clutch I5 and relay 62 are energized simultaneously, so that in the energized condition unit 66 is electrically disconnected from unit 64 and is mechanically connected to unit 61. Under these conditions airspeed indicator I! is controlled, through shaft I4, clutch I5 and shaft I06, by motor 96, and its position is thus determined by the rotated position of winding 651) with respect to winding a.

Operation of relays 60, BI and 62 and clutch I5 is initiated and interrupted by a second operation of manual knob 51, which functions through a 'disk IUI of insulating material, or through other suitable means, to make connection between a pair of normally open contacts I62 and I63. Contact I02 is connected to conductor 36. Contact I63 is connected through a conductor I64 to. one terminal of each of relays 60, 6| and 6 and of clutch I5. The other terminals of these relays and the clutch are connected to conductor 21 as shown in Figure 1. Knob 51 is mounted for limited axial movement, to permit disk IIII to cause contact I63 to engage contact I02. When this happens the relays and clutch are actuated, air-speed indicator I1 is disconnected from air-speed sensing unit I2, and control of the voltages on windings 61b and III) is transferred from motor 8| acting through unit III to knob 51 acting through unit 65: at the same time the mechanical connection is completed between units 66 and 61 for controlling air speed indicator II.

In addition to controlling the position of slider 45, rebalancing motor II also acts to provide a first mechanical input I06 to a differential I01. A second mechanical input I II] is provided to differential I61 from a timer or clock III, which also provides a mechanical input I I2 to drive time indicator I4. Connection I'I2 may include, if desired, a suitable slip friction device II3 to permit resetting of indicator I4 by a suitable knob I I4. The output from differential III'I is supplied as at II5 to indicator I5. This output may also include a slip friction device II6 to permit resetting of indicator I5 by a suitable manual knob III.

In brief review, present time is displayed on panel board I3 by indicator I4, by direct connection to timer III. Estimated time of arrival is displayed by indicator I5 on panel board I3, by the joint effect of timer II I' and rebalancing Operation of motor II is determined by the value ofdistance to destination, which controls the position of slider 3| in balanceable it, the value of ground speed, which determined the position of slider '44 The distance to destination input is supplied through shaft 22 directly by converter 20. The ground speed input is supplied through motor 4.2,, and-isindisated on panel. boa-rd 1.3 at H5. -Operation of motor I2 is controlled alternatively either by manual knob 55!, or by motor 81 in smoother 99, which in turn is energized from converter 2.0. Air speed is indicated at .11 on panel board .43 this indication is. normally controlled by airspeed sensing unit 12.; alternatively by :motor 96., which is alternatively controllable either from motor .81 :or from manual knob 51. When motor $5 is controlled from motor 8],, howevergno use is made of its output, since at this time clutch "i5 disengaged. The normal condition of the system is that existing when knob 5! is not depressed. When the :knob is depressed, relays .60, 6] and 2 and clutch are energized, thus maleing control of motors l2 and 96, and hence of indicators 46 and I1 and slider 34, dependent upon the rotation of manual knob 57. When the knob is allowed to resume its undepressed condition, the normal association of parts will resume, and the telemetric systems again rebalance themselves in their former positions.

Before proceeding to a detailed description of the operation of the system, further consideration must be given to the structure oi units 2e, 2 l and 22, in so far as it bears on an understanding of the present invention. v

The term Distance Measuring Equipment hereafter will be abbreviated as D. M. E., and

refers to specific radio apparatus known in the art by that name, and described in the report of the Third. Commonwealth and Empire Conference on Radio for Civil Aviation, 1945, pages 197 to 205. It should be appreciated, however, that the use of this particular device in the present application is illustrative only, and that other suitable device, such for example as a navigating computer, whichgives as outputs thedistance to destination and the ground speed of a craf may be used with equal satisfaction.

Interrogator l9 emits spaced radio signalsfrQm a transmitting antenna system H7. These signals reach the receiving antenna system 120 of responder 2|, and each signal causes the responder to emit a radio signal from a transmitting antenna system 121', which in turn reaches the receiving antenna system 122 of interrogator IS. The delay in responder 23 between reception of a signal and transmission .of a signal in response thereto is known, so that the time interval between the transmission of a signal from the interrogator and the subsequent reception at the interrogator of the resulting signal from the responder is proportional to the distance between the two units, if reduced by the delay time. The time interval is converted in intcrrogator 19 to a voltage from which are derived by converter 2-0, a mechanical shaft rotation proportional to the distance and a second voltage proportional to the derivative of the distance, that is, to the ground speed of the craft measured in the direction of the responder.

Converter 26 is shown in Figure 2 with related portions of interrogator IS. The output of the latter is conventionally a voltage applied to a high impedance voltmeter: the purpose of the converter is to derive .irom this voltage a shaft rotation proportional thereto, without destroying the accuracy of the original system. The interrogator is shown at I9, belowand to the aci -m left of the dotted line 28; and the voltage in question is impressed on :a meter 1-32,, one side of which is connected to the plate of a .pentode i3 5 and the other sideof which is connected to the source of plate voltage. The resistance of the pentode is varied by voltages impressed on its control electrodes, by means, not shown, provided therefor, in accordance with the distance being measured, and thus the voltage between 'theposit-iyc terminal of the power supply and the .pla-teis-also varied.

The .most sati'siactory method of motor control is one using a rebalancing or null type of network: such a network must be so designed that the measuring circuit .is not loaded down thereby to-a point where its accuracy is destroyed. This accomplished according .to the present invention by a comparison arrangement in which first the voltage across the meter and then a comparison voltage is applied to an amplifier of high input resistance, and the amplifier energizes a motor to adjust the comparison voltage to equality with the voltage being measured. The motor shaft rotation also comprises the mechanical output from the converter, since it .is a measure of the comparison voltage, which is in turn proportional to the distance being measured.

in order to minimize the effect of change in the supply voltage, the comparison voltage is obtained from the same source. Thus a first conductor .134 .is connected to the positive terminal I of the power supply and a second conductor L35 is connected to ground, which is the negative terminal of the power supply, at i3'l. In series between these two conductors there are connected a first variable resistor Hit a potential divider HI having a slider l i2 movable with respect to a linear winding [43, and a second variable resistor 1M. The values of resistors M6 and 114 are adjusted so that when meter E32 gives -its maximum reading slider M2 is at the same potential as 'the negative terminal of the meter if the slider is at the left hand end of winding I 43, and'w'hen meter I32 gives its minimum reading slider 142 "is at the same potential as the meter terminal if at the right hand end of the winding: resistors M0 and HM are thus centering means coordinating the range of slider M2 with the range of voltage available across pentode I33.

The converter includes an interrupter M5 having a winding .145, a movable contact Mr, and a pair of fixed contacts 150. and "E51. Winding I46 is energizedfrom source 2'5 through conductor 30, ground connections I52 and l 53, a conductor 54, a capacitor I55, and conductor 2? to cause movable contact 141 to oscillate between fixed contacts I50 and r51 at the frequency of the source. Fixed contact its is connected to the negative terminal of meter [32 by a conductor 1%, and fixed contact I51 is connected to slider M2 by conductor I551. The potential of movable contact 'IAl 'isthus alternated between that of fixed contact 158 and that of fixed contact I51, and if the two fixed contacts are not at the same potential a square wave alternating voltage of the freqiwncy of the source appears upon movable contact M7, and is applied to an amplifier it through capacitor 158, conductors I61 and 1G2, and ground. Qperation of movable contact M1 is maintained in phase with the voltage supplied by confluctors 27 and 30 by means of phasing capacitor 155. A grounded resistor J59 cooperates with a blocking capacitor 158 to separate the A. O. and D. C. input circuits to the amplifier,

Amplifier I60 i of the type in which a voltage is obtained at output terminals I63 and I61 which is of the same phase, positive or negative, and the same frequency as the voltage applied to input terminals I64 and I65. The output voltage is impressed by conductors I10 and HI upon one winding I12 of a two phase motor I13 having a second winding I14 and a rotor I15. The power factor of the motor may be improved by the addition of a capacitor I16 across winding I12. Winding I14 is energized from source 25 through conductor 30, ground connections I52 and I11, phasing capacitor NH, and conductor I80 and 21.

Unitary on the shaft I82 of motor I13 is the rotor I 83 of a velocity generator or dynamic transformer I84. This generator has an energizing winding I85 and an output winding I80, the former being energized from source 25 through conductor 30, ground connections I52 and I81, phasing capacitor I9I and conductors I90 and 21. Winding I85 is connected in the input circuit of amplifier I00, which may be traced from terminal IE4 through conductors I02 and I 6|, capacitor I53, movable contact I41, fixed contact I 50 (or I5I), pentode I33 (or slider I42,-a portion of winding I43, and variable resistor I44), ground connections I31 and I81, winding I86, and conductor I92 to input terminal I65.

The output voltage of velocity generator I84 is also supplied to a pair of output terminals IBM and 202 by ground connection-s I81 and I91 and conductors I92 and I96.

The shaft I82 of motor I is connected through reduction gearing I93 to a shaft I04 which actuates the slider I42 along winding I43. Input shaft 22 to the computer is also coupled to motor shaft I82, through reduction gearing I95.

Operation The mode of operation of the structure described above will now be readily understood, reference first being made to Figure 2. For illustration suppose first that a craft is fixed at a point 80 miles from a particular transmitter. In norma1 operation of the D. M. the voltage across meter I32 varies substantially linearly with distance from the station, so that for example the voltage may be 125 volts when the craft is 100 miles from the station and 26 volts when the craft is 1 mile from the station. The voltage between terminal I 35 and ground is fixed at say 275 volts, so that the voltage between ground and the plate of the pentode, and hence between ground and fixed contact I50, may vary from 249 volts, when the craft is one mile from the station, to 150 volts, when the craft is 100 miles from the station. Under these conditions the voltage with respect to ground on fixed contact I50, when the craft is 80 miles from the station, is 230 volts. Resistors I40 and I 44 are adjusted so that their values and that of winding I43 are in the ratio of 25, 100 and 150 respectively: the potential at the terminals of winding I43, connected to resistors I40 and resistor I44 respectively, are 250 and 150 volts respectively measured to ground.

Slider I42 has by the prior operation of the system been set at some position along winding I43; if this position happens to be at four-fifths of the length of the winding from the junction point with resistor I44, the slider is at a potential of 150+ (100) volts, or 230 volts, with respect to ground, and fixed contact I5I is at this potential. Fixed contact I50 is also at this potential,

of 230 volts and one of say 240 volts.

by reason of operation of the D. M. E., and movable contact I41, in moving from fixed contact I to fixed contact I5I, encounters no change in potential, but remains at a uniform voltage with respect to ground. The movable contact is so adjusted as not to disengage both fixed contacts at the same time, always engaging one contact just before disengaging the other. The fixed voltage between movable contact I41 and ground is prevented from reaching amplifier I60 by blocking capacitor I 58: the amplifier is hence deenergized and no operation of motor I13 takes place. Slider I42 remains where it is, shaft 22 does not rotate, and no voltage appears between contacts 20l and 202.

If theposition of slider I42 is not four-fifths of the length of the winding from the junction point with resistor I 44, the slider is at some other potential than 230 volts with respect to ground. If the slider is too near the junction point with resistor I40, fixed contact I 5I is at a potential higher than fixed contact I50, and movable contact I41 alternates between a potential to ground This in effect applies a square wave voltage of 5 volts peak amplitude to the input of amplifier I00 through capacitor I58, which as before blocks out the continuous 235 volt component of the square Wave. The frequency of the square wave is that of source 25, since the vibrator is energized from that source and operates synchronously-with it.

The fundamental component of the square wave is amplified and impressed by amplifier I60 on winding I12 of motor I13. By reason of phasing capacitor I the movement of vibrator I45 is brought into a desired phase relation with the voltage of the source suchthat under the foregoing conditions the voltage across winding I12 is exactly in phase for example with the voltage of the source. The voltage across winding I14, on the other hand, lags that of the source by 90, by reason of quadrature capacitor IBI. Motor I13 is constructed, as is well known in the art, so that when windings I12 and I14 are energized with alternating voltages in quadrature, a rotating field is set up and the motor operates,

' the direction of operation being determined by I60 from movable contact I41 decreasing at the same time. I

When motor I 13 begins to operate, velocity generator I84 begins to supply an output voltage.

This generator is of the type which supplies an.-

output increasing in amplitude but not in frequency as the speed at which it is driven, in-l The arrangement is basically a transcreases. former of which winding I85 comprises the primary and winding I the secondary, the trans fer of energy between the windings being substantially zero for no rotation of the rotor and increasing as the speed of the rotor increases. The voltage output from secondary winding I is brought into substantiall80 phase relation to the voltage at source 25 by phasing capacitor HM, and is connected into the input circuit of amplifier I60 in such a fashion as to oppose the voltage from movable contact I41.

The actual input voltage to the amplifier 15 thus reduced by the output of the velocity gencrater, in turn reducing the. output from the amplifier the amount of energization of the motor. A condition of equilibrium is reached in for a constant signal Voltage, the motor runs at a constant rate such that the constant output from the velocity generator combined with the signal voltage gives a constant input voltage to the amplifier. For a uniiormly decreasing distance voltage, the condition of equilibrium is that in which the motor moves at a uniform speed such that the output from the velocity generator combined with the signal voltage which represents the difierence between the distance voltage on contact [50 and the rebalance voltage on contact i5l, gives a uniform input voltage to the amplifier. If the motor runs at a faster speed, the velocity generator output voltage increases, reducing the signal to the amplifier and so slowing down the motor; If the motor runs at a slower speed the signal voltage increases, increasing, the signal to the amplifier and so speeding up the motor. The velocity generator output voltage is determined by the turns ratio and the amplitude of the voltage supplied to the primary winding- If the slider M2 happens to be toonear the center of winding M3 instead of too near the junction point with resistor M0, fixed contact 55h is at a potential lower than fixed contact I56, and movable contact l4! alternates between a potential to ground of 230 volts and one of. said 220 volts. The movable contact engages the' respective fixed contacts at the same points in the cycle of source 25 as before, but now the relative polarities of the contacts is reversed and the square wave transmitted to amplifier Hill through capacitor ['58 is of the opposite phase to that previously described. The phase of the output of amplifier Hill accordingly reverses, reversing the phase of the voltage across winding I12 of motor 173-. The phase of winding I'M remaining constant; this results in reversal of the op-- eration of motor H3, moving slider M 2 to the right as seen in Figure 2 toreduce the voltage difierence between fixed contacts I50 and IN to zero, and also reversing the direction of operation of shaft 22 and the phase of the output of velocity generator F84, so that it can again cooperate in opposition with the signal voltage/to ive antihunt operation of the system.

The output voltage of velocity generator [8'4 is not only applied to amplifier Hill to give anti-hunt properties to the system, but is also applied to terminals 20! and 2-02. The initial operation of the system thus far disclosed takes place very rapidly, and is preliminary to the operation of the system in use, which will now be described.

Heretofore it has been assumed that the craft is at a point fixed in space. Actually, of course, this is not true: the craft is moving and its motion has a component in the direction of the line joining the craft and the station. If the craft is moving along the line, there is no other component, and this is contemplated as the preferable mode of operation of the invention. The airspeed of a craft is normally maintained constant by the pilot, and hence for a constant wind the distance from the transmitter to a craft approaching the transmitter decreases at a uniform rate. This means that the voltage on fixed contact I50 also decreases at a constant rate, and that for the equilibrium conditions in the amplifier input-output system the motor must run at such a constant rate as will give a constant input signal to the amplifier to energize the motor- The velocity generator output voltage, being proportional to the speed of the motor, accordingly a measure of the rate of change of distance to the transmitter, or of ground speed toward the station.

The amount of rotation of shaft 22 is a measure of the actual distance of the craft from the transmitter, the slight droop in the system required to continuously energize motor E13 being negligible. Converter 28 thus supplies a mechanical output at shaft 22 proportional to the distancefrom the craft to the responder, and an electrical output proportional to the rate of change of that distance. If the air speed changes the rate of movement of slider M2 and shaft 22 becomes proportional to the new air speed.

Referring now to Figure 1, the terminals 20! and 262 and the shaft 22 of converter 20 are shown associated with elements of the computer. Shaft 22 is shown as driving slider 3|: when theposition of shaft 22 corresponds to a distance of- 100 miles between the craft and the transmitter, slider 3! is at the right-hand end of winding 33, and the slider moves from one end of the winding to the other as the position of shaft 22 moves intocorrespondence with a distance of 0 miles between the craft and the transmitter. This relation is brought about by selection of a proper ratio for reduction gearing I93 and I95 of Figure 2.

The voltage at terminals 2M and 202 comprises a ground speed input to the computer, and is to determine the rotated position of winding 10b. To accomplish this the ground speed signal is opposed by a rebalance signal derived from voltage divider 80, the position of whose slider is determined concurrently with the position of winding Nib by operation of motor 8!. The ground speed signal is further opposed by a velocity-proportional signal from velocity generator Tl associated with motor 8i. If for any given voltage appearing at terminals 201 and 202 there is a voltage between conductor 23 and slider 83 equal and opposite thereto, no input voltage is supplied to amplifier 16, no energization of motor 8% and no change in the position of slider 33 occurs and no output is supplied by velocity generator Tl. Winding 1% therefore remains in the same position, and a voltage from winding 10a is inductively supplied theret-hrough to winding 'Hb, fixed in position by motor [2, and hence inductively to amplifier 92 depending. on the rotated position of winding 1 lb.

For a unique position of the latter winding the voltage transmitted to winding Ha is zero, amplifier 92 is not energized, no operation of motor [2 occurs, and slider 44, winding 'IIb and indicator [6 remain in the same positions. For any other position of winding 1 lb the voltage induced. in winding 1 la energizes amplifier 92, and operation of motor l2 is initiated, in a direction to rotate winding 'Hb so as to decrease and finally remove the signal in winding Ha: when this has been accomplished, operation of motor i2 ceases and slider 44 and counter is remainin the new positions to which the operation of the motor has brought them.

If the voltage between slider 83 and conductor 23' is not equal and opposite to that between terminals 202 and 201, a resultant voltage appears as an input to amplifier 16, which energizes motor 8| as described in connection with motor I13. The motor operates until slider 83 has taken some new position in which the two voltages become equal, at the same time rotating winding b with respect to winding 10a. 'Velocity generator TI acts as described in connection with generator I84, to give the system antihunt properties; however, the turns, ratio and excitation of velocity generator 11 are chosen to give a higher output voltage than is needed merely to prevent hunting. As consequence, the response of motor iii to rapid changes in the input signal on conductors 23 and 24 is reduced, thus giving a smoothing effect.

Rotation of winding 1022 results in a different distribution of voltages of the winding, and hence in winding I Ib. A voltage is induced in winding Ha which is of the proper phase to cause operation of motor I 2 in a direction to move slider 44 to the right if movement of slider 83 to the right is being caused by motor 8|, and to increase the reading of indicator I6.

Slider 44 is to be moved from one end to the other of winding 42 when the ground speed varies between zero and some selected maximum value such as 300 M. P. H., being in contact with the end of the winding connected to conductor 3'! for zero ground speed, and the indications of indicator I6 are also to vary through the same range at the same time. Movement of slider 83 from one end of winding 84 to the other corresponds to variation in the voltage between terminals 25! and 202 from zero to a value proportional to 300 M. P. H., and occurs simultaneously with rotation of winding Illb through 360 or less. This rotation requires the same angular rotation of winding 'iIb to maintain the output from winding Ha constant, and this rotation of winding 'Ilb must be accomplished during movement of the slider 44 the length of winding 42, and must be accompanied by movement of indicator It between readings of zero and 300 miles per hour. In order to accomplish this, mechanical connections 56, 9|, and 94 may include reducing gearing of the necessary ratios, the ratio of reducing gearing I9 being considered.

The system is set up so that, for a known ground speed of the craft, as determined in any suitable manner, the ground speed indicated by indicator I6 is correct, and the displacement of slider 44 along winding 52 from conductor 31 has the same relation to the total available displacement of the slider as does the known ground speed to 300 M. P. H.

Whenever winding 10b is rotated, the same change in voltage distribution which effects winding IIb as described above also eifects Winding 51b, and in the same fashion a voltage is induced in winding 61a energizing amplifier 95 to cause operation of motor 95 in a direction to reduce the induced voltage to zero. When this has been done rotation of motor 96 stops. The rotation of the motor drives one side of clutch 15, but since the latter is in its deenergized condition no change in the system as a whole results.

In order that network In may be consistent within itself, and operate on the same scale," proper values must be selected for the voltages applied to windings 33 and 82. Assuming a scale of 1 volt per mile, the voltage output from trans former 35 must be 100 volts; assuming a scale of one volt per M. P. H., the voltage output from transformer 41 must be 300 volts. Accordingly, movement of slider 45 from one end of winding 43 to the other end represents a range for Ta, the time until arrival, of O to 1 hour.

In the balanceable network the voltage between slider 3l and conductor 31 is proportional to lip The voltage bgtween slider 45 and .con-

ductor 31 is a portion of y'p, that between slider 44 and conductor 31, determined by the ratio of the displacement of slider 55 from conductor 31 to the total available displacement of the slider. The ratio just named is proportional to the Ta in Equation 1 on the same basis that the voltages from sliders 3I and M to conductor 31 are proportional to 11p and 22 respectively. The difference between the voltages from sliders 3i and 45 will be zero only when slider 45 is brought to a position where the equation is satisfied. When this condition prevails there is no input to amplifier 53, motor II is not actuated, and slider 45 remains motionless. For any other voltage relationship, motor II is energized for operation in a direction to move slider 45 so that the voltage difference becomes zero, at the same time supplying a mechanical input through differential I Ill to drive indicator I5.

Before the system is put into operation on any flight, clock III must be in operation and indicator I4 set to the correct time by knob I I4. The clock drives indicator I5 through difi'erential I01, and this indicator must also be set to correct time by knob I I1. Thereafter when this system is put into operation as described above, motor II is operated to balance network I0 and simultaneously adjusts indicator I5 through differential I01, adding to the reading of the indicator an amount Ta so that indicator I5 now gives estimated time of arrival. Mechanical connections 55 and I06 may be provided with suitable reduction gearing to make this possible. As the craft continues in flight for an interval th Tp component of estimated time of arrival is continuously corrected by clock I I I, and the Ta component is continuous- 1y corrected by motor II.

Air-speed indicator I I is actuated by operation of motor 66, in accordance with the responses of air-speed sensing unit I2. For any value of air speed there is a unique position of winding 64b and hence a unique distribution of voltages from winding 64a to winding 6%. The same voltage distribution is conductively supplied to winding 66b, and since windings 34a and 66a are energized from the same source, winding 66b is caused to rotate into the same position as winding 64b. Suitable reduction gearing may be provided in mechanical connections 74 and 18, to cause the air-speed indicator ll to read the actual air speed as sensed by unit 12. From the structure thus far described it is apparent that indications are obtained on panel board I3 of the present time, the estimated time of arrival at a given destination, the ground speed being made good toward the destination and the indicated air speed. The estimation of time of arrival is of course dependent on the assumption that ground speed toward the transmitter will continue at the rate presently prevailing. If by reason of unanticipated head winds the craft does not approach the transmitting station as rapidly as was anticipated, the reading on indicator IE will decrease, and that on indicator I5 will increase faster than that on indicator I4, thus indicating a later estimated time of arrival. Normally the pilot would exercise his power to change his groundspeed and restore the desired estimated time of arrival but conditions may arise when this becomes impossible. Under these conditions it may be necessary for the pilot of the craft to establish communications with the control operator at the airport of destination, indicating that he will not be able to make good his estimated time of arrival and requesting the assign- 1 5 ment of a new time of arrival which will permit him to land without interference with the operation of other craft in the vicinity.

Upon being assigned a new estimated time of arrival, it is desirable that the pilot be able to determine in a quick and. simple manner whether or not it is within the capabilities of his craft to make good the new estimated time of arrival. The latter may be found to require speed from the craft which it is incapable of supplying, or it may require the craft to slow down to such an extent that if simple straight line flight were continued the safety of the craft and its occupants would be in danger, so that circling or some other time consuming maneuver should be begun. The method by which the pilot may make such determinations will now be explained.

Suppose the conditions of flight of -a craft are those shown in the panel board in Figure 1,:and suppose further that the pilot is contacted by the trafiic control officer at the destination and is instructed to change his operation to make good an estimated time of arrival of 13:57

The board shows a ground speed of 184 miles per hour and a diiference in time of 1-6 minutes between the present time and the estimated time of arrival: this means that the craft is 49 miles from its destination. To see whether the new estimated time of arrival can be achieved, the pilot simply pushes knob 5'! to the right .as seen in Figure 1, simultaneously rotating the knob and Watching indicator H5.

The axial movement of knob 5'5 engages contacts H12 and it, the circuit energizing relays 60, GI and 52 and clutch 15. Operation of relay 62 disconnects winding- 66b from energization by winding 641): thus although winding 65a is still energized no force acts to rotate shaft 14. Operation of relay 6i! disconnects winding 6512 from energization by winding Nib. Operation of relay Bl disconnects windings Nb and Nb from energization by winding WI), and connects them instead for energization by winding 65b. Energization of clutch l5 mechanically connects shafts I4 and Hit, so that rotation of winding 61b re sults in rotation of winding 6% and adjustment of indicator H.

Transfer of control of windings Nb and 61b from winding 102) to winding 55b has no immediate effect, since until relay 50 was operated winding 65%; was electrically maintained in step with winding 59b, which controlled windings fi'ib and Nb. However, when knob 51' is now rotated the distribution of voltages in winding 65b is altered and these voltages, appearing at wind.- ings Nb and 67b, cause rotation of these windings. Amplifier at is energized, motor l2. op.- erates to adjust winding 'Hb to a new position in which the voltage induced in winding H; is zero, indicator it is set to a new reading, and slider M is adjusted to a new position on winding 42. By this means the voltage across winding 43 is changed, the input to amplifier 53 is no longer zero, and motor H is energized to adjust. slider 45 until the input becomes zero, and to alter the reading of indicator 55. This process is continued until indicator i reads 13:57 as assigned: for this condition indicator [-6. readsv 294 M. P. H.

Amplifier 95 is also energized, causing operation of motor 96 to rotate winding 6111 until the input to the amplifier is zero, and driving shaft 14, winding 66b, and indicator H. The circuits for motor l2 and 9B are equivalent, so that for each mile per hour change in the reading of, in.-

31:6 dicator l6 brought about by motor [2, a change of lmile per hour in the reading of indicator I1 is brought about by ;motor 96. The panel board now gives readings of 13:57, 294, and 282 for estimated time of arrival, ground speed, and air speed respectively. The pilot observes indicator lL-concludes that it is impossible for him to opcrate his craft at-such .an air speed, and requests another assignment of estimated time of arrival. He also releases knob 57, which permits disengagement of contacts 102 and I03 by means of any suitable spring or other arrangement, thus deenergizing relays 60, 6!, and 62 and clutch 15.

During this periodwinding 3% has been maintained in a position representative of indicated airspeed 'by-sensing unit 12, and winding liih has been maintained in .a position representative of ground speed by motor 81: windings b, 66b, 61b and Nb have been rotated out of positional agreement with windings 64b and 101), from which they have been disconnected. Deenergization of the relays now restores the connections between windings 65b and winding 6%, and also restores the connections between winding 1% and windings 65b, 61b, and lib. Deenergization of clutch 15 removes the interconnection between windings 66b and 61b. The various telemetric systems now return to the positions shown in Figure 1, except that lapse of time changes the readings of indicators M. This process may be repeated until an estimated time of arrival within the capabilities of the craft is assigned, after which-the air speed of the craft must be changed by the pilot until the newly assigned estimated time of arrival is shown on indicator I5.

In the foregoing specification I have clearly described apparatus shown in the drawing for determining the estimated time of arrival of a craft moving toward a destination where there is .a D. E. responder, by means responding automatically to a D. M. E. interrogator in the craft to give outputs proportional to the crafts ground speed and its distance from the destination. I have also shown adjuncts to the above apparatus making it possible to determine in a simple manner, without mental or other computations, whether any assigned estimated time of arrival can :be achieved by the craft under the conditions of distance and time remaining, and the known operating limits of the craft. The relationship between the invention as a whole and known components such as the D. M. E. has been clearly pointed out and shown in the drawing, and numerous advantages and objects of the invention. havev been discussed. The disclosure, however,.-is illustrative only, and I may make changes in detail, within the principle of the invention, to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.

I claim as my invention:

1.. In. a device of the class described, in combination: means responsive to the ground speed of a craft in a selected direction; means responsive to the distance, in said direction, from a craft to a destination; an indicator; a balanceable system including components adjustable in accordance with the responses of said responsive means and a further component variable to balance said network for various adjusted conditions of said components; means responsive to present time; and means actuated by said last named means and by any unbalance of said system to simultaneously rebalance said system and operate said indicator to an indication. of the 17 estimated time of arrival of said craft at said destination.

2. In a device of the class described, in combination: means supplying a first voltage varying only with ground speed; means supplying a second voltage proportional to distance to a destination, means comparing a variable portion of said first voltage with said second voltage; means adjustable to vary the magnitude of said portion until it is equal to said second voltage, so that the magnitude of said portion is a measure of the interval before the destination is reached; a timer; and means actuated in accordance with the magnitude of said portion and with the operation of said timer for indicating the estimated time of arrival at said destination.

3. In a device of the class described, in combination: a Distance Measuring Equipment installation including an interrogator and a responder; means deriving from said interrogator signals proportional to its distance from said responder and to the rate of change of said distance; a timer; indicators of ground speed and estimated time of arrival; means normally operating said ground speed indicator from the rate of change signal of said interrogator; and means operating said estimated time of arrival indicator in accordance with operation of said timer and said ground speed indicator and with the distance signal from said interrogator.

4. In a device of the class described, in combination: means giving an output proportional to the air speed of a craft; means giving an output proportional to the ground speed of said craft; means giving an output proportional to said crafts distance to a destination; means giving an output proportional to present time; means actuated in accordance with the three last named outputs to compute the crafts estimated time of arrival at said destination; means displaying said air speed, said ground speed, and said estimated time of arrival; and means actuable to substitute an arbitrary output for said second named output for bringing said displayed estimated time of arrival to a desired value, and to simultaneously vary said displayed ground speed and air speed by equal amounts.

5. In a device of the class described in combination: a ground speed indicator, an air speed indicator; means normally operating said indicators in accordance with the ground speed and air speed respectively of a moving craft; and means including a manually operable member for first interrupting said normal relation and then causing simultaneous operation of both said indicators.

6. In a device of the class described in combination: a ground speed indicator, an air-speed indicator; means normally operating said indicators in accordance with the ground speed and air speed respectively of a moving craft; an estimated time of arrival indicator; means giving an output proportional to the distance to the destination of the craft; means operating said last named indicator in accordance with said output and with operation of said ground speed indicator; and means interrupting said normal relation and independently causing simultaneous operation of said ground speed indicator and said air-speed indicator, to bring said estimated time of arrival indicator to a desired indication.

'7. In a device of the class described, in combination: a distance measuring equipment installation including an interrogator; means deriving from said interrogator signals proportional to its distance from a point of destination and to' the rate of change of said distance; a timer; an air-speed sensing unit; indicators of air speed, ground speed, and estimated time of arrival; means normally operating said air-speed indicator from said air-speed sensing unit; means normally operating said ground speed indicator from the rate of change signal of said interrogator; means operating said estimated time of arrival indicator in accordance with operation of said timer and said ground speed indicator and with the distance signal of said interrogator; and means operable to prevent said air-speed sensing unit and said interrogator rate of change signal from affecting said air-speed and ground speed indicators and to independently operate said indicators simultaneously to indications corresponding to a desired indication of estimated time of arrival.

8. In a device of the class described, in combination: an air-speed responsive device; an airspeed indicator; means normally connecting said indicator for operation by said device; means giving a, signal proportional to ground speed; a ground speed indicator; means normally connecting said ground speed indicator for operation by said signal; means giving an output proportional to distance to destination; a balanceable network including first and second impedance means, variable in accordance with said distance output and with the operation of said ground speed indicator respectively, and motor variable impedance means; motor control means regulating the operation of said motor to adjust said motor adjusted impedance means so as to balance said network; timing means; an indicator of estimated time of arrival; means connecting said last named indicator for operation by said motor and said timing means; a manually operable member; and means actuated upon operation of said member to disable said first and second named connecting means and to cause simultaneous operation of said air-speed indicator and said ground speed indicator independent of actual air speed and ground speed, to cause a desired change in said estimated time of arrival indicator.

9. In a device of the class described, in combination: means giving an output proportional to the air speed of a craft; means giving an output proportional to the ground speed of said craft; means giving an output proportional to said crafts distance to a destination; means giving an output proportional to present time; means actuated in accordance with the three last named outputs to compute the craft's estimated time of arrival at said destination; means displaying said air speed, said ground speed and said estimated time of arrival; means effective when actuated to substitute an arbitrary output for said second named output, for bringing said displayed estimated time of arrival to a desired value, and to simultaneously vary said displayed ground speed and air speed by equal amounts, and effective when deactuated to cause return of said displayed quantities to their former values.

10. In a device of the class described, in combination: means giving an output proportional to the ground speed of said craft; means giving an output proportional to said crafts distance to a destination; means giving an output proportional to present time; means actuated in accordance with said outputs to compute the crafts estimated time of arrival at said destination; means displaying said present time, said ground speed, and said estimated time of arrival; and means actuable to substitute an arbitrary output for said first named output for bringing said displayed estimated time of arrival to a desired value, and to simultaneously vary said displayed ground speed.

11. In a device of the class described, in combination; a ground speed indicator; means normally operating'said indicator in accordance with the ground speed of a moving craft; an estimated time of arrival indicator; means giving an output proportional to the distance to the destination of the craft; means operating said last named indicator in accordance with said output and with operation of said ground speed indicator; and means interrupting said normal relation and independently causing operation of said ground speed indicator, to bring said estimated time of arrival indicator to a desired indication.

OSCAR HUGO SCHUCK.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Hewlett et a1 July 26, 1927 Huebner et al Mar. 19, 1935 Williams Apr. 5, 1938 Riggs Apr. 26, 1938 Thurlow Feb. 16, 1943 Sanders Feb. 18, 1947 Harris Aug. 12, 1947 Sanders, Jr Dec. 16, 1947 Field et a1 Oct. 11, 1949 Herbst Mar. 14, 1950 Fennessy et a1 Jan. 15, 1952 

